Automatic gauge control for rolling mills



Feb. 3, 1970 R. H. ELLIS I 3,492,848

v AUTOMATIC GAUGE CONTROL FOR ROLLING MILLS Filed Aug. 22, 1967 1 INVENTOR.

M8547 ELL/5 BY Qz am Anne/v94 United States Patent 3,492,848 AUTOMATIC GAUGE CONTROL FOR ROLLING MILLS Robert Hunter Ellis, Pittsburgh, Pa., assignor to United Engineering and Foundry Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 22, 1967, Ser. No. 662,516 Claims priority, applicatirir lGr/efia Britain, Sept. 19, 1966,

4 Int. CLB21b 37/08 US. Cl. 72-21 5 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an automatic gauge control system for a rolling mill and, more particularly, to a system adapted to produce constant longitudinal gauge in a rolling mill or like apparatus.

More particularly, the present invention provides a control system for employment in an hydro-mechanical type of rolling mill, whereby the gauge correction necessary by reason of a change in rolling load is accomplished by operating both a hydraulic and a mechanical roll adjusting mechanism, such as, a hydraulic force applicator cylinder and a mechanical screwdown.

In one form, the present invention provides a rolling mill, for example, a 4-high mill, wherein there is provided hydraulic means adapted to vary the gap of the rolls of the mill and adapted to apply a prestressed force in a direction to oppose the separating force of the mill, wherein said prestressed force is at all times greater than the separating force, first control means for effecting a first adjustment of the roll gap by adjusting the prestressed force when there is experienced a change in separating force to maintain the ditference between the separating force and prestressing force constant, a mechanical screwdown adapted to vary the gap of the rolls of the mill, means for producing a signal representing the rolling force, means for producing a signal rep-resenting the elastic coeflicient of the mill parts not subject to prestress, means for producing a signal representing the initial setting of the rolls before the separating force is developed, a second control means for receiving said signals and producing a resultant signal representing the thickness of the material being rolled and comparing this signal with a representation of desired thickness to produce an error signal, means for relating the error signal to the mechanical screwdown to effect a second adjustment of the roll gap.

The present invention relates to an improvement to mill control system described in British Patent No. 955,164 dated Apr. 15, 1964. In this patent, there is illustrated a 4-high mill, which involves mechanical screws arranged "between the backup chocks for separating the chocks and defining the initial roll gap of the mill. The screws are associated with load cells which measure a part of a prestressed force applied to the backup chocks by means of a piston cylinder assembly located at the bottom of the mill, the pressure being maintained at all times greater than the expected rolling load. In operation, an initial prestressed lead is imposed upon the load cells before rolling occurs. During rolling the separating force tends to displace the screws away from the cells, thereby producing a signal intended to represent the amount of the displacement of the work rolls. This signal is employed to vary the prestressed force so as to maintain the cell reading constant. In effect this design attempts to maintain the distance between the axes of the back-up rolls constant. This, of course, has the effect of canceling out the elastic change of the housing and the backup chocks from influencing the gauge of the material. However, it does not compensate for the elastic change in the bending and flattening backup rolls and the flattening and compression of the work rolls.

Still another form of prior art is illustrated in US. Patent No. 2,726,541. This patent teaches a way to determine the actual gauge at the bite of the rolls by solving the formula where T is the actual gauge, S is the initial roll setting in the absence of any separating force, F is the rolling force, and M is the elastic constant of the rolling mill not including the prestressed elements. This formula is solved by an electrical apparatus and the result compared with the desired thickness to produce an error signal. The error signal is then used to vary the position of the rolls. In practice, however, it has been found that due to the large inertias involved to efliect a screwdown adjustment, an objectionable time lapse is experienced between the time a gauge error is detected and a correction is made.

These objections of the prior art in each instance are overcome by the present invention, one form of which is illustrated in the accompanying drawing diagrammatically showing a 4-high rolling mill.

With reference to this drawing there is illustrated a 4-high rolling mill consisting of a pair of housings, one of which is shown at 10 which has a window 11 into which there is received a pair of backup chocks 12 and 13 for rotatably supporting a pair of backup rolls 14 and 15, the adjacent surfaces of the chocks have openings for receiving the pair of work roll chocks 16 and 17 which rotatably support work rolls 18 and 19. Between the bottom backup chock 13 and the top of the housing 10 there extends a pair of compression rods 22 which pass unrestrictedly through the top backup chock 12, the lower end of the rods are adapted to engage load cells 23, one of which is shown in the drawing. These load cells may follow the form of many commercial units presently available on the market. The top chock 12 is adapted to be adjusted according to ordinary mill construction by a screw 24 which is rotatably received in a nut 25 mounted in the housing 10, the upper end of the screw being provided with a wheel 26 which engages a worm 27, the worm being driven by a motor 28, whereby the top rolls are adjusted vertically. Referring to the bottom of the mill, the lower chock is adapted to be engaged by the piston of the piston cylinder assembly 29 mounted between the housing 10 and the bottom work roll chock. It will be appreciated that what has been said with respect to the housing illustrated is true with respect to the other housing, not shown, and for which reason it has not been deemed necessary to describe it.

It should be noted, as mentioned with respect to the aforesaid British patent, that the piston cylinder assembly is adapted to prestress the mill by providing a force opposing the separating force generated between the work rolls 18 and 19, the prestressed force when no material in the mill being read by the load cells 23 which are forcibly engaged by the compression rods 22. When mill receives the material, the reading of the load cells drops causing a signal to be sent to the cylinder assembly 29 to raise the force it exerts until the cell reading is raised to its initial reading. In effect the cylinder establishes a constant relationship between the separating force and the prestressing force, which relationship is maintained by varying the force of the prestressed cylinder as the separating force varies.

As noted previously, the varying pressure of the cylinder pursuant to a change in the reading of the cell tends to maintain the backup rolls at a constant distance. However, this does not take care of any of the elastic changes due to the deflection and flattening of the backup rolls or compression of the work rolls, backup chocks, screw and nut assembly.

It is an object of the present invention to provide a separate, but coordinate gauge control system which will work in conjunction with the control of the prestressed hydraulic cylinder so that the elastic change of the above-mentioned elements will be compensated for.

In this regard there is provided a system for determining the difference between the actual gauge of the strip and the desired gauge at the bite of the rolls and for adjusting the screwdown pursuant to the difference to correct for it. In reference again to the drawing, it will be noted that the signal from load cell 23 is adapted to be transferred to an amplifier 32, the amplifier also receives a load cell reference signal from a potentiometer 33 and produces a signal that is sent to a servovalve 34 that varies its output. The servovalve is fed from a pump 35 which is driven by a motor 36. The servovalve system serves to feed pressurized fluid to the bottom of the cylinder assembly 29, thereby adjusting the pressure pursuant to the load cell signal so as to maintain the aforesaid constant relationship between the separating force and the prestressed force.

The load cell signal is also sent to an amplifier 37 from which a negative signal is sent to a second amplifier 38, which also receives a second load signal representing the pressure of the piston cylinder assembly 29 from a load cell 41 located beneath the cylinder assembly. It will be appreciated that in place of a load cell 41, a pressure transducer could be arranged in the cylinder assembly line. The amplifier 38 receives, therefore, the negative signal representing the pressure imposed upon the load cell 23 and the pressure of the cylinder assembly 29 and added together to produce a signal that represents the actual rolling load of the mill. It will also be appreciated that a load cell placed under the screw and nut assembly above the top backup chock would measure this rolling load directly and the signal from which would be sent directly to an amplifier 42. The amplifier 38 sends a signal representing the rolling load F to a second amplifier 42 where it is combined with a signal M generated by a potentiometer 43, representing the co efficient of elasticity of the parts subject to the rolling loads but not including the prestressed elements. The amplifiers 42 produces a signal representing F/M which represents the ratio of the force over the elastic constant of the mill M in accordance with the aforesaid formula The F/M signal is sent to an amplifier 44 where it is joined with two other signals, namely a signal S produced from a potentiometer 45 which represents the desired strip gauge and a signal S produced by a potentiometer 46 which is the initial setting of the roll gap without there being any material in the mill. The amplifier 44, therefore, produces a signal representing that a difference exists between the actual gauge and the desired gauge. Any such difference is represented by an error signal that is sent by the amplifier 44 to the screwdown motor 28 and which will operate the motor until the error signal is reduced to zero.

From the above it can be seen that the combined hydraulic and mechanical gauge control networks are brought together to work as an integral system thereby to correct for the entire elastic change of the mill, and from which a constant gauge can be obtained. It will also be appreciated by those skilled in the art that other forms of the present invention can be utilized without departing from the scope of the invention.

It will be appreciated that the various amplifiers illustrated in the drawing are of the typical, well-known design as exemplified in a publication by Korn and Korn, entitled Electric Analog Computers, published by Me- GraW Hill, 1952.

In accordance with the provisions of the patent statutes, I have explained the principle and operation of my invention and have illustrated and described what I consider to represent the best embodiment thereof. However, I desire to have it understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A control system for maintaining an established roll gap between a pair of working rolls supported by housing means of a rolling mill for reducing strip material,

said working rolls constituting at least a part of a first group of related mill parts adapted to receive a separating force developed by the working rolls in reducing the strip material,

hydraulic means for developing a prestressing force upon a second group of related mill parts which includes at least a part of said housing means,

said hydraulic means being constructed and arranged in said housing to vary the gap of said working rolls,

said prestressing force being greater in magnitude than said separating force and in a direction opposing the separating force,

said first group of related mill parts being characterized by the fact that they are not subject to the prestressing force and further that when subject to a varying separating force, there results a variation in the roll gap,

first control means for effecting a first adjustment of said roll gap by adjusting said hydraulic means when there is experienced a change in the separating force thereby to maintain a constant difference between the separating force and the prestressing force, mechanical means for establishing a desired roll gap, means for producing a first signal representing the separating force between said rolls,

means for producing a second signal representing the elastic coefficient of said first group of related mill parts,

means for producing a third signal representing the desired roll gap established before development of said separating force,

second control means for receiving said first, second and third signals and producing a resultant signal representative of the actual thickness of rolled strip material,

means for producing a fourth signal representative of the desired thickness of material after rolling,

said second control means further producing an error signal derived by comparing said resultant signal with said fourth signal, said error signal being employed to actuate said mechanical means for varying said roll gap to effect adjustment of the roll gap in accordance with the derived error signal.

2. A control system according to claim 1, wherein said resultant signal produced by said second control means is derived by solving the formula:

where T equals the actual thickness of strip after rolling, S equals the roll gap setting in the absence of said separating force, F equals the separating force and M equals elastic coeificient of said first group of related mill parts.

3. A control system according to claim 2, wherein said first group of related mill parts comprises:

said mechanical means for establishing a desired roll upper and lower backup rolls for supporting said working rolls, and

a chock for rotatably supporting said upper backup roll.

4. A control system according to claim 3, wherein said second group of related mill parts includes:

a chock for supporting said lower backup roll, and

compression spacer means arranged between said lower chock and said housing means.

5. In combination with a rolling mill having a housing,

a pair of Working rolls received in said housing and between which a roll gap is established for performing a reduction on material fed between the rolls,

a mechanical power means arranged in said housing for adjusting the roll gap,

a rapid-action hydraulic force applying means adapted to adjust the gap of the rolls by applying a controllable force in a direction to oppose a separating force of the rolls and wherein said controllable force is at all times greater than the separating force.

certain mill parts being subject only to the separating force and other mill parts being subject only to the difference between the separating force and said controllable force,

a control system for producing a primary signal and a monitory signal, which in concert represent the total change in the roll gap of the mill due to a change in the separating force, said control system comprising:

means located in said housing arranged to be subject to the difference between said controllable force and said separating force for producing a first signal When a pre-established difference between the separating force and the prestressed force varies,

means for receiving said first signal and for effecting a primary corrective adjustment of said roll gap by causing said hydraulic means to re-establish the preestablished difference between the separating force and the controllable force,

means for producing a second signal proportional to the total separating force,

means for producing. a third signal representing the elastic coefficient of said mill parts subject to the separating force,

means for producing a fourth signal representing the initial roll gap established before any separating force is created,

means for producing a fifth signal representative of the desired thickness of the material after rolling,

means for receiving said second, third and fourth signals and producing a resultant signal representative of the actual thickness of rolled material,

said last named means further producing a monitory signal derived by comparing said resultant signal with said fifth signal, and

said monitory signal being employed for effecting a monitory adjustment of the roll gap by causing operation of said mechanical power means until the actual thickness and the desired thickness coincide.

References Cited UNITED STATES PATENTS 3,327,502; 6/1967 Brown 72-243 CHARLES W. LANHAM, Primary Examiner 0 L. A. LARSON, Assistant Examiner us. 01. X.R. 

